Medical transdermal patches have many uses, for example in hormone replacement, anti-anginal, travel sickness and smoking cessation therapy. Although various types of transdermal patches have been used, it is now generally preferred to use a patch which has a backing sheet and one or more layers, including an adhesive layer which attaches the patch to the skin. The adhesive layer is typically a viscous liquid containing at least one active component. The patch is supplied on a release-liner covering the adhesive, which is peeled off immediately before applying the patch to the skin. The active component then passes through the skin.
It is known to package such patches in a polymer or multi-layer laminate envelope or sachet. WO 95/00122 (published Jan. 5, 1995, after the priority date now claimed), shows an example of this, in which a release liner carrying four patches is enclosed in a resealable bag made of plastic film or foil laminate. A modified package is known from Japanese Utility Model publication 1-155428 (accepted publication no. 4-51782) in which the patch is mounted on a release liner provided with raised dimples to minimise contact between the envelope or sachet and the patch. A similar package has been marketed, for example, by Ortho-Cilag under the name Evorel.TM.. It has been found that although the raised dimples provide a limited degree of protection, they do not prevent pressure on the patch due to handling, leading to oozing of the viscous adhesive which forms a sticky ring around the patch. This results in a tendency for the patch to stick to the envelope or sachet.
It is also known to provide a blister-pack in which a patch attached to a release liner, which is the same size as the patch itself, is located in a shallow blister formed between a plastic moulding and a foil lidding. A rib is formed around the blister, to increase rigidity of the otherwise fragile pack which is susceptible to curling. Such a patch is believed to have been marketed under the name TRIALSAT.TM. by Beta Pharmaceuticals.
Use of a release liner which is the same size as the patch means that the only sticky part of the patch is at the periphery, though adhesive can ooze around the edges of the patch. However, because the patch and release liner are the same size, it can be difficult and messy to separate the two. It may be undesirable that the active component is touched by a user, except at the intended application point. Furthermore, the need for a reinforcing rib around the blister increases the overall size of the package, so that the package occupies a much larger volume than the patch itself.